Shooting hoses filled with carbon dioxide into the confinement houses, metal boxes and "kill carts" causes the birds to burn, freeze, and suffocate to death simultaneously - and slowly. This is the egg industry's main method of exterminating "spent" hens, whether from battery cages or cage-free confinement operations, with or without bird flu. 
As for fire-fighting foam, which the US Department of Agriculture approved in 2006, contrary to the lie that the birds are dead within a minute of being blanketed under the foam, Bruce Webster of The University of Georgia told a USDA meeting in June 2006: "You saw a lot of escape behavior for 4 to 6 minutes. You saw the birds' heads sticking out of the foam." Eventually, their movements ceased, as the birds were "worn out" with their "volitional struggle," Webster told attendees including myself at the meeting. 
In a firefighting foam trial with turkeys, birds were reported flapping under the foam for up to 6 minutes. This does not mean that the turkeys were unconscious or dead when the flapping stopped or appeared to stop. And foam-covered birds cannot vocalize their suffering. They cannot be seen or heard. Necropsies showed hemorrhages in the tracheas of birds who died under the foam, and "occlusion of the trachea by the foam" was cited by Ruth Newberry of Washington State University as "a serious welfare concern."